CA1254270A - Phase-locked loop - Google Patents
Phase-locked loopInfo
- Publication number
- CA1254270A CA1254270A CA000496913A CA496913A CA1254270A CA 1254270 A CA1254270 A CA 1254270A CA 000496913 A CA000496913 A CA 000496913A CA 496913 A CA496913 A CA 496913A CA 1254270 A CA1254270 A CA 1254270A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- phase
- phase difference
- local clock
- supplement
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000013589 supplement Substances 0.000 claims abstract description 17
- 230000007704 transition Effects 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 3
- 238000004891 communication Methods 0.000 description 3
- 241000272470 Circus Species 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
- H04L7/033—Speed or phase control by the received code signals, the signals containing no special synchronisation information using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
- Synchronisation In Digital Transmission Systems (AREA)
Abstract
ABSTRACT
A phase-locked loop which is controllable irrespective of the kind of input signal is described. A random two-level code sequence derived from a clock signal having a predetermined fre-quency is applied as an input signal. A voltage controlled oscillator generates a local clock signal. In response to the local clock pulse, a discriminator latches the input signal to produce a discrimination signal. An exclusive-OR gate produces a first phase difference signal from the input signal and the discrimination signal. A phase supplement signal generator, res-ponsive to the first phase difference signal and the local clock pulse, produces a phase supplement signal. Responsive to the first phase difference signal and the phase supplement signal, a control signal generator produces a control signal to control the voltage controlled oscillator.
A phase-locked loop which is controllable irrespective of the kind of input signal is described. A random two-level code sequence derived from a clock signal having a predetermined fre-quency is applied as an input signal. A voltage controlled oscillator generates a local clock signal. In response to the local clock pulse, a discriminator latches the input signal to produce a discrimination signal. An exclusive-OR gate produces a first phase difference signal from the input signal and the discrimination signal. A phase supplement signal generator, res-ponsive to the first phase difference signal and the local clock pulse, produces a phase supplement signal. Responsive to the first phase difference signal and the phase supplement signal, a control signal generator produces a control signal to control the voltage controlled oscillator.
Description
~S~2 ~
PHASE-LOCKED LOOP
BACKGROUND OF THE INVENTION
The present invention relates to a phase-locked loop which is supplied with a random two-level code sequence derived from a clock pulse having a frequency f0 to generate a local clock pulse which is synchronous to the clock pulse in phase and frequency.
A phase-locked loop (PLL) is often needed in, typically, a timing circuit built in a receive section of a data modem, ~nd a timins circuit built in a repeater which is used in a pulse code modulation (PCM) communication system.
Recently, this type of PLL has come to be used in a timing circuit of a device which is designed to retrieve data from a digital recording medium.
A PLL of the type described is supplied with a random two-level code sequence and provided with a different configuration from an ordinary PLL which serves to synchronize a local clock pulse to an externally supplied clock pulse. Specifically, where the input signal to a PLL is a clock pulse which is supplied from the outside, a phase difference between the input signal and a local clock pulse is detectable by, for example, providing exclusive-OR of the input signal and the local clock pulse so that phase-locking may be accomplished by controlling
PHASE-LOCKED LOOP
BACKGROUND OF THE INVENTION
The present invention relates to a phase-locked loop which is supplied with a random two-level code sequence derived from a clock pulse having a frequency f0 to generate a local clock pulse which is synchronous to the clock pulse in phase and frequency.
A phase-locked loop (PLL) is often needed in, typically, a timing circuit built in a receive section of a data modem, ~nd a timins circuit built in a repeater which is used in a pulse code modulation (PCM) communication system.
Recently, this type of PLL has come to be used in a timing circuit of a device which is designed to retrieve data from a digital recording medium.
A PLL of the type described is supplied with a random two-level code sequence and provided with a different configuration from an ordinary PLL which serves to synchronize a local clock pulse to an externally supplied clock pulse. Specifically, where the input signal to a PLL is a clock pulse which is supplied from the outside, a phase difference between the input signal and a local clock pulse is detectable by, for example, providing exclusive-OR of the input signal and the local clock pulse so that phase-locking may be accomplished by controlling
- 2 -~ ~ 5~
a voltage controlled oscillator (VCO) responsive to the phase difference. However, where the input signal is a random two-level code sequence, the exclusive-OR output of the input signal and the local clock pulse fluctuates due to the statistical characteristic of a two-level code sequence, preventing an accurate phase difference from being detected.
Heretofore, various approaches have been proposed to eliminate the arawback which is particular to such an ordinary PL1 as discussed. One of them is a PLL which is described by Ross C. Halgren in a paper entitled "Improved Acquisitio~ ~ n Phase-Locked Loops with ~awtooth Phase Detectors", IEEE Transactions on Communications, Vol.COM-30, No. 10, October 1982. However, the PLL scheme described in this paper has the disadvantage that when a pattern having a repetition frequency of fO/4 arrives, a signal whose frequency is one half the frequency of a local clock pulse necessarily appears at an output terminal to practically disable the control of the phase-locking.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a PLL which settles the above-discussed problematic situation and is controllable with no regard to the kind of an input signal.
In accordance with the present invention, there is provided a phase-locked loop to which a random two-level _ 3 - ~ 2~ 7~
code se~uence derived from a clock signal having a predetermined frequency is applied as an input signal.
A voltage controlled oscillator generates a local clock signal. In response to the local clock pulse, a discriminator latches the input signal to produce a discrimination signal.
An exclusive-OR gate produces a first phase difference signal from the input signal and the discrimination signal.
A phase supplement signal generator, responsive to the first phase dif~erence signal and the local clock pulse, produces a phase supplement signal. Responsive to the irst phase difference signal and tke phase supplement signal, a control signal generator produces a control signal to control the voltage controlled oscillator.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a PLL embodying the present invention; and Figs. 2A to 2H show waveforms demonstrating the operation of the PLL shown in Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figs. 1 and 2A-2H, a random two-level _ 4 _ 125427~
code sequence (Fig. 2B) which is derived from a clock (Fig. 2A) at a transmission side is applied to a latch circuit or discrimination circu:it 102 and an exclusive-OR
gate 103. The latch circuit 102 latches the two-level code sequence in response to rising edges of local clock pulses (Fig. 2C) which is generated by a voltage controlled oscillator (VCO) 107. The exclusive-OR gate 103 gives an exclusive-OR operation in response to an output of the latch circuit 102 (Fig. 2D) and the two-level code sequence, thereby producing a phase difference signal ( ig. 2E) indicative of a phase difference between the trans~ission clock pulse and the local cIock pulse.
As shown in Fig. 2E, at least when a data transition has occurred, a phase difference between the transmission clock pulse and the local clock pulse is detected.
However, the waveform shown in Fig. 2E includes those low-level sections 1001 -1004 which have no phase difference information and develop as a result of absence of data transitions. Hence, if the phase difference signal is directly applied to a VCO as a control signal, the control of the VCO falls into inaccuracy due to the absence of phase difference information in those low-level sections. In accordance with the present invention, a phase supplement signal generator is provided for generating a phase supplement signal (Fig. 2G) which supplements phase difference information associated with the low-level _ 5 ~ iL~
sections concerned, using the phase difference signal of Fig. 2E. The phase supplement signal generator comprises a D-type flip-flop 104, and an AND gate 105 for providing an AND operation of an output of the flip-flop 104 (Fig. 2F) and the local clock pulse. The phase supplement signal (Fig. 2G) outputted by the ~ND gate 105 is applied to an adder 106 to be added to the phase difference signal rrom the exclusive-OR gate 103 (Fig. 2H). The output of the adder 106 is fed to the VCO 107 as a control signal.
The VCO 107, responsive to the phase difference output of the adder 105, controls the frequency of the local clock pulse such .nat the phase difference between the local clock pulse and the transmission clock pulse becomes zero.
As stated above, it will be seen that the present invention provides a PLL which performs all the steps up to the detection of absence of data transition by a digital technique and the supplement of phase information to transition-lacking sections by analog addition. Hence, whatever the statistical characteristic of the input random two-level code sequence may be, a phase difference is positively detected at least when a data transition has occurred and phase information is positively supplemented in the transition-lacking sections. This allows the PLL
to be surely controlled all the time. In addition, discrimination of the input signals and synchronization of the local clock pulse are implemented with a simple - 6 - ~25~
circuit arrangement such as shown in Fig. 1, the PLL of the present invention is feasible for large scale integration.
While the phase difference signal has been shown and described as being directly applied to a VCO, it may be routed thereto through a loop filter to be made s~oother.
This and other modifications to the circuit construction rall in the scope of the present invention.
Although the input signal has been represented by a two-level random sequence, iL naturally covers other codes such as CMI codes and DMI codes which are extensively used in an optical communications -ield.
a voltage controlled oscillator (VCO) responsive to the phase difference. However, where the input signal is a random two-level code sequence, the exclusive-OR output of the input signal and the local clock pulse fluctuates due to the statistical characteristic of a two-level code sequence, preventing an accurate phase difference from being detected.
Heretofore, various approaches have been proposed to eliminate the arawback which is particular to such an ordinary PL1 as discussed. One of them is a PLL which is described by Ross C. Halgren in a paper entitled "Improved Acquisitio~ ~ n Phase-Locked Loops with ~awtooth Phase Detectors", IEEE Transactions on Communications, Vol.COM-30, No. 10, October 1982. However, the PLL scheme described in this paper has the disadvantage that when a pattern having a repetition frequency of fO/4 arrives, a signal whose frequency is one half the frequency of a local clock pulse necessarily appears at an output terminal to practically disable the control of the phase-locking.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a PLL which settles the above-discussed problematic situation and is controllable with no regard to the kind of an input signal.
In accordance with the present invention, there is provided a phase-locked loop to which a random two-level _ 3 - ~ 2~ 7~
code se~uence derived from a clock signal having a predetermined frequency is applied as an input signal.
A voltage controlled oscillator generates a local clock signal. In response to the local clock pulse, a discriminator latches the input signal to produce a discrimination signal.
An exclusive-OR gate produces a first phase difference signal from the input signal and the discrimination signal.
A phase supplement signal generator, responsive to the first phase dif~erence signal and the local clock pulse, produces a phase supplement signal. Responsive to the irst phase difference signal and tke phase supplement signal, a control signal generator produces a control signal to control the voltage controlled oscillator.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a PLL embodying the present invention; and Figs. 2A to 2H show waveforms demonstrating the operation of the PLL shown in Fig. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figs. 1 and 2A-2H, a random two-level _ 4 _ 125427~
code sequence (Fig. 2B) which is derived from a clock (Fig. 2A) at a transmission side is applied to a latch circuit or discrimination circu:it 102 and an exclusive-OR
gate 103. The latch circuit 102 latches the two-level code sequence in response to rising edges of local clock pulses (Fig. 2C) which is generated by a voltage controlled oscillator (VCO) 107. The exclusive-OR gate 103 gives an exclusive-OR operation in response to an output of the latch circuit 102 (Fig. 2D) and the two-level code sequence, thereby producing a phase difference signal ( ig. 2E) indicative of a phase difference between the trans~ission clock pulse and the local cIock pulse.
As shown in Fig. 2E, at least when a data transition has occurred, a phase difference between the transmission clock pulse and the local clock pulse is detected.
However, the waveform shown in Fig. 2E includes those low-level sections 1001 -1004 which have no phase difference information and develop as a result of absence of data transitions. Hence, if the phase difference signal is directly applied to a VCO as a control signal, the control of the VCO falls into inaccuracy due to the absence of phase difference information in those low-level sections. In accordance with the present invention, a phase supplement signal generator is provided for generating a phase supplement signal (Fig. 2G) which supplements phase difference information associated with the low-level _ 5 ~ iL~
sections concerned, using the phase difference signal of Fig. 2E. The phase supplement signal generator comprises a D-type flip-flop 104, and an AND gate 105 for providing an AND operation of an output of the flip-flop 104 (Fig. 2F) and the local clock pulse. The phase supplement signal (Fig. 2G) outputted by the ~ND gate 105 is applied to an adder 106 to be added to the phase difference signal rrom the exclusive-OR gate 103 (Fig. 2H). The output of the adder 106 is fed to the VCO 107 as a control signal.
The VCO 107, responsive to the phase difference output of the adder 105, controls the frequency of the local clock pulse such .nat the phase difference between the local clock pulse and the transmission clock pulse becomes zero.
As stated above, it will be seen that the present invention provides a PLL which performs all the steps up to the detection of absence of data transition by a digital technique and the supplement of phase information to transition-lacking sections by analog addition. Hence, whatever the statistical characteristic of the input random two-level code sequence may be, a phase difference is positively detected at least when a data transition has occurred and phase information is positively supplemented in the transition-lacking sections. This allows the PLL
to be surely controlled all the time. In addition, discrimination of the input signals and synchronization of the local clock pulse are implemented with a simple - 6 - ~25~
circuit arrangement such as shown in Fig. 1, the PLL of the present invention is feasible for large scale integration.
While the phase difference signal has been shown and described as being directly applied to a VCO, it may be routed thereto through a loop filter to be made s~oother.
This and other modifications to the circuit construction rall in the scope of the present invention.
Although the input signal has been represented by a two-level random sequence, iL naturally covers other codes such as CMI codes and DMI codes which are extensively used in an optical communications -ield.
Claims (2)
1. A phase locked loop to which a random two-level code sequence signal derived from clock pulses having a predetermined frequency is applied as an input signal, comprising:
voltage controlled oscillator means for generating local clock pulses;
discriminator means responsive to said local clock pulses for producing a discrimination signal;
means for producing a first phase difference signal between the input signal and the discrimination signal;
phase supplement signal generating means responsive to the first phase difference signal and the local clock pulses for producing a phase supplement signal; and means responsive to the first phase difference signal and the phase supplement signal for producing a control signal to control the voltage controlled oscillator.
voltage controlled oscillator means for generating local clock pulses;
discriminator means responsive to said local clock pulses for producing a discrimination signal;
means for producing a first phase difference signal between the input signal and the discrimination signal;
phase supplement signal generating means responsive to the first phase difference signal and the local clock pulses for producing a phase supplement signal; and means responsive to the first phase difference signal and the phase supplement signal for producing a control signal to control the voltage controlled oscillator.
2. A phase locked loop as claimed in claim 1, wherein said phase supplement signal generating means comprise a D-type flip-flop responsive to said first phase difference signal for producing a local signal, and an AND gate responsive to the local signal and the local clock pulses for producing said phase supplement signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59257842A JPS61135250A (en) | 1984-12-06 | 1984-12-06 | Phase locking circuit |
| JP257842/1984 | 1984-12-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254270A true CA1254270A (en) | 1989-05-16 |
Family
ID=17311898
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000496913A Expired CA1254270A (en) | 1984-12-06 | 1985-12-05 | Phase-locked loop |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4642575A (en) |
| JP (1) | JPS61135250A (en) |
| AU (1) | AU575285B2 (en) |
| CA (1) | CA1254270A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0779366B2 (en) * | 1989-10-26 | 1995-08-23 | 株式会社東芝 | Terminal device connected to the communication network |
| US5252865A (en) * | 1991-08-22 | 1993-10-12 | Triquint Semiconductor, Inc. | Integrating phase detector |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57203213A (en) * | 1981-06-08 | 1982-12-13 | Trio Kenwood Corp | Clock signal reproducing circuit |
| FR2511563B1 (en) * | 1981-08-14 | 1986-05-16 | Trt Telecom Radio Electr | PHASE LOCKING DEVICE FOR PROVIDING SIGNALS WHOSE FREQUENCY MAY VARY ON A WIDE RANGE |
| US4535459A (en) * | 1983-05-26 | 1985-08-13 | Rockwell International Corporation | Signal detection apparatus |
-
1984
- 1984-12-06 JP JP59257842A patent/JPS61135250A/en active Pending
-
1985
- 1985-12-05 CA CA000496913A patent/CA1254270A/en not_active Expired
- 1985-12-06 US US06/805,536 patent/US4642575A/en not_active Expired - Lifetime
- 1985-12-06 AU AU50856/85A patent/AU575285B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4642575A (en) | 1987-02-10 |
| AU575285B2 (en) | 1988-07-21 |
| JPS61135250A (en) | 1986-06-23 |
| AU5085685A (en) | 1986-06-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |